Salts of triarylsulfonium and a fluorine-containing anion (BF4, PF6, AsF6, SbF6, etc.) have been known as polymerization initiators having a high photocationic polymerization initiation capability.
Among proposed sulfonium salt manufacturing methods, there is known, for example, a method including condensing a sulfide and a sulfoxide in the presence of at least one of an inorganic acid such as sulfuric acid and a strong organic acid such as methanesulfonic acid and subsequently exchanging an anion derived from the strong organic acid for a fluorine-containing anion (for example, see Japanese Unexamined Patent Application Publication No. 61-100557). In this method, there is produced a monosulfonium salt having one sulfonio group in one molecule, as well as a bissulfonium salt having two sulfonio groups in one molecule.